The present invention relates to the modification of microbial cellulose during its synthesis by cellulose-producing microorganisms. This modification results from the presence of a substance which alters the formation of native cellulose structure. The prototypical structure-modifying substance is carboxymethylcellulose.
Cellulose may be produced by microorganisms of the Acetobacterium, Rhizobium, Alcaligenes, Agrobacterium, and Pseudomonas type (see, for example Brown, Jr. et al. J. Applied Polymer Science: Polymer Symposium (1983) V.37 pp 33-78). The growth of cellulose-producing microorganisms with production of cellulose may occur when said microorganisms are aerobically cultivated in an appropriate nutrient medium.
Appropriate nutrient media of the present invention generally include standard nutrient medium such as GYC which contains (g/liter of distilled water): yeast extract, 10.0; D-glucose, 50.0; CaCO.sub.3, 30.0 and agar, 25.0. Various alternatives such as replacements for glucose or yeast extract, and omissions of agar or CaCO.sub.3 are usable and well-known to those skilled in the art (Bergey's Manual of SYSTEMATIC BIOLOGY Vol. 1 pp 268-276, Krieg, ed. Williams and Wilkins, Baltimore/London (1984). The preferred nutrient medium used directly or with modifications described herein was that first described by Schramm and Hestrin (Hestrin et al. Biochem. J. Vol. 58 pp 345-352 (1954). The standard Schramm Hestrin (SH) medium contained (g/L): D-glucose, 20; peptone, 5; yeast extract, 5; dibasic sodium phosphate, 2.7, and citric acid monohydrate, 1.15 (pH adjusted to between about 3.5 and 5.5 with HCl). When Schramm Hestrin without glucose (SH-gluc) is designated, this indicates the above SH composition, but without the 10 g glucose/liter addition.
The cellulose produced by Acetobacter xylinum (formerly known as Acetobacter aceti subsp. xylinum and reclassified by the 1984 Bergy's Manual cited above as a subspecies of Acetobacter pasteurianus and Acetobacter hansenii) has been widely studied. In the present application the primarily studied cellulose-producing microorganism is termed "Acetobacter xylinum". It is understood that these several names may be used to indicate the same organism.
Fibrillar alterations of microbially-produced cellulose by agents such as CMC have been previously shown to occur, for example, by ultrastructural studies using techniques such as electron microscopy (Haigler et al., J. Cell Biology, Vol. 94 pp 64-69 (1982) and Ben-Hayim et al. J. Cell Biology, Vol. 25 pp 191-207 (1965)). However, nowhere before the present invention has any substance been found or suggested to facilitate the microbial production of a cellulose with greatly improved and/or unique macroscopic properties such as resiliency, elasticity, tensile strength, degree of water absorptivity or retention of absorbtive capacity after repeated wettings.
Cellulose assembled by a static aerobic culture of Acetobacter xylinum may be contained in a hydrophilic membrane known as a pellicle. This cellulose is quite strong when wet, but brittle when dried. One of the major obstacles in using the natural absorbency of this native bacterial cellulose has been its inability to effectively retain absorbancy through cycles of wetting and drying. In an effort to improve the physical properties of the cellulose, the present invention concerns including a cellulose derivative such as carboxymethylcellulose in the culture medium during microbial synthesis of cellulose. This inclusion altered the produced cellulose to result in a product which retained most of its native absorbancy through cycles of wetting and drying. One object of this invention is to significantly alter the physical properties of microbial cellulose product by cellulose derivatives or related substances in order to expand the material uses of this product. It is envisioned that there will be, for example, tremendous advantages in the uses of this product in the absorbent technology industries.